Plural sample ion source

ABSTRACT

An ion source for separately ionizing a plurality of vaporized samples and focusing the ions produced by the ionization into an ion beam containing ions from each of the vaporized samples. The ion source comprises an ionization chamber having an aperture through which ions are emitted, means for emitting an electron beam into the ionization chamber, at least one ion control electrode for establishing an ion control field, and partition means for dividing the ionization chamber into a first and second electron bombardment chamber. The ion source also includes a first and second gas storage vessel for respectively introducing at least a first and second vaporized sample into the first and second electron bombardment chambers, respectively, so that the first and second vaporized samples are independently ionized.

PLURAL SAMPLE ION SOURCE Inventor: Michael J. Wallington, Manchester,

England Assignee: Associated Electrical Industries Limited, London,England Filed: Nov. 12, 1969 Appl. N0.: 876,078

Foreign Application Priority Data Dec. 17, 1968 Great Britain 59940/68us. c1 250/424, 250/285, 250/423, 250/427, 313/63 1111. C1. H0lj 39/34Field of Search. 250/41.9 G, 41.9 SB, 41.9 SE

References Cited UNITED STATES PATENTS 11/1956 Dietz 250/41.9

11/1967 Jenckel 250/41.9 10/1968 Wanless et a1 250/41.9

57021465 VE55EL.

[ Nov. 19, 1974 Primary Examiner-William F. Lindquist Attorney, Agent,or Firm-Watts, Hoffmann, Fisher & Heinke Co.

[57] ABSTRACT An ion source for separately ionizing a plurality ofvaporized samples and focusing the ions produced by the ionization intoan ion beam containing ions from each of the vaporized samples. The ionsource comprises an ionization chamber having an aperture through whichions are emitted, means for emitting an electron beam into theionization chamber, at least one ion control electrode for establishingan ion control field, and partition means for dividing the ionizationchamber into a first and second electron bombardment chamber. The ionsource also includes a first and second gas storage vessel forrespectively introducing at least a first and second vaporized sampleinto the first and second electron bombardment chambers, respectively,so that the first and second vaporized samples are independentlyionized.

14 Claims, 2 Drawing Figures STORAGE V5555!- 5UPPLY HOUSE DE TEC T02PLURAL SAMPLE ION SOURCE BACKGROUND OF THE INVENTION This inventionpertains to the art of ion sources and, more particularly, to improvedion sources for independently ionizing a plurality of gas samples.

Known ion sources have included an ionization chamber into which twodifferent gas samples are introduced in order to ionize the samples byelectron bombardment. Generally, one of the gas samples is a referencesample of which the spectral peaks are of a known mass, and the othersample is an unknown sample in which the spectral peaks thereof are tobe compared with those of the reference sample. The molecules of the gassamples are ionized by an electron beam which passes through thechamber, and the ions produced by this ionization process are thenfocused and accelerated by a series of electrodes so that the ions areprojected through an ion exit slit in the ion source. When such ionsources are employed in a mass spectrometer system, the projected ionsare directed into a magnetic analyzer of the spectrometer.

In these mass spectrometer systems, it is desirable to maintain the ioncurrent of each of the gas samples at a relatively high value. In orderto obtain an ion current of a relatively high level, it is necessary toincrease the value of the ionizing electron beam current, oraltematively, it is necessary to increase the total pressure of the twosamples in the ionization region. It has been found, however, that whenthe ionizing electron beam current is sufficiently high and the totalpressure of the two samples in the ionization region exceeds a certaincritical value, an increase in the partial pressure of one of the gassamples causes a decrease in the number of ions produced from the othersample. Thus, when the reference sample is introduced into theionization chamber, i.e., an increase in the partial pressure of thereference sample, the number of ions of the unknown sample present inthe ion beam decreases. This decrease in the number of ions developed bythe unknown sample whenever the reference sample is introduced into theionization chamber results in a decrease in the intensity of thespectral peaks of the unknown sample, thereby resulting in measurementerrors.

More particularly, it has been found that if nitrogen is present in anionization chamber at a pressure exceeding a certain critical value, thenitrogen ion current in the ion beam decreases approximatelyexponentially as the pressure of another sample, such as heptacosafluoro tributylamine, is linearly increased.

SUMMARY OF THE INVENTION The present invention is directed toward an ionsource in which a plurality of vaporized samples may be independentlyionized, thereby overcoming the noted disadvantages, and others, of suchprevious ion sources.

In accordance with one aspect of the present invention, the ion sourcefor separately ionizing a plurality of gas samples comprises anionization chamber having an aperture for the passage of ions, means foremitting an electron beam into the ionization chamber for developingions by electron bombardment, at least one ion control electrode forestablishing an ion control field, and partition means for dividing theionization chamber into a first and second electron bombardment chamber,so that a first and second gas sample may be independently ionized. Apair of gas storage vessels are respectively associated with the firstand second electron bombardment chambers so that the first and secondgas samples may be separately introduced into the electron bombardmentchambers.

In accordance with another aspect of the present invention, there isprovided, in a mass spectrometer, an ion source having an ionizationchamber for separately .ionizing a plurality of vaporized samples. Theionization chamber includes an evacuatable chamber having an aperturefor the passage of ions, means for dividing the evacuatable chamber intoat least a first and second electron bombardment chamber, means foremitting an electron beam into the ionization chamber for developingions by electron bombardment, and means for establishing an iontransporting field for propelling the ions through the aperture so thatthe ions are directed into an ion beam. A pair of passage means areprovided for introducing a first and a second gas sample into the firstand second electron bombardment chambers, respectively, so that thefirst and second gas samples are independently ionized.

In accordance with still another aspect of the present invention, theelectron beam emitting means includes a pair of electron emittingelements for respectively emitting a first electron beam into the firstelectron bombardment chamber and a second electron beam into the secondelectron bombardment chamber so that the first and second vaporizedsamples are separately ionized by the pair of electron beams.

In accordance with a still further aspect of the present invention, theion source includes means for evacuating air from the first and secondelectron bombardment chamber.

In accordance with another aspect of the present invention there isprovided a method of generating an ion beam containing ions from aplurality of vaporized samples. The steps in accordance with this methodinclude, introducing a first and second vaporized sample into a firstand second electron bombardment chamber, separately ionizing the firstand second vaporized sample in the first and second electron bombardmentchambers respectively to thereby generate ions from the vaporizedsamples, and, accelerating the ions produced from both of the vaporizedsamples through an aperture means to thereby form a single ion beam.

The primary object of the present invention is to provide an ion sourcehaving an ionization chamber for separately ionizing a plurality ofvaporized samples.

Another object of the present invention is to provide an ion sourcewherein the ionization chamber includes partition means for dividing theionization chamber into a plurality of separate electron bombardmentchambers so that a plurality of gas samples may be independentlyionized.

A further object of the present invention is to provide an ion sourcewherein at least two gas samples are separately ionized. and the ionsdeveloped upon ionization of the two gas samples are then focused intoan ion beam.

A still further object of the present invention is to provide anionization chamber wherein at least two vaporized samples may be ionizedin a manner such that an increase in the partial pressure of one of thesamples has substantially no effect on the number of ions developed bythe other vaporized sample.

Another object of the present invention is to provide an ion sourcewherein at least two gas samples may be ionized in such a manner suchthat an increase in the partial pressure of one gas sample hassubstantially no effect on the ionization of the other sample.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantagesof the invention will become apparent from the following description ofthe preferred embodiment of the invention as read in conjunction withthe accompanying drawings in which:

FIG. 1 is a block diagram, sectional view of an ion source illustratinga preferred embodiment of the present invention; and,

FIG. 2 is a sectional view of the ion source illustrated in FIG. 1,taken along line 2--2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,FIG. 1 illustrates a mass spectrometer 10, which generally comprises anevacuatable chamber 14 which encloses an ionization chamber 12 and acollector assembly 13. The ionization chamber 12 includes an aperture 16for the passage of ions, and a partition wall 18 which divides theionization chamber 12 into a pair of electron bombardment chambers 20,22. The aperture 16 is defined by a pair of chamber walls 23, 25, eachof which has a leading edge 27, 29, which slopes away from the aperture16. The walls 23, 25 are electrically insulated from the remainder ofelectron bombardment chamber 20, 22, and each of the wall 23, 25 iselectrically connected to voltage supply source 8-]. The edge 31 ofpartition wall 18 tapers to a point so as to direct the ions through thegenerally funnel shaped aperture 16. Ionization chamber 12 iselectrically connected to a voltage sup ply S-l. Positioned withinelectron bombardment chamber 20 is a generally arcuate shaped ionrepeller electrode 24, which is electrically connected to a voltagesupply source S-l. Similarly, positioned within electron bombardmentchamber 22 is a generally arcuate shaped ion repeller electrode 26 whichis electrically connected to voltage supply source 8-1.

The electron bombardment chambers 20, 22 are respectively coupled to apair of gas storage vessels 28, 30, electrically insulated fromionization chambers 20 and 22, so that a first and second gas sample maybe introduced into the electron bombardment chambers 20, 22. Also, anelectron beam 32 is emitted into electron bombardment chamber 20 by theflow of the electrons between a cathode 34 and an anode 36 through apair of apertures 38, 40 in electron bombardment chamber 20. The cathode34 and anode 36 are connected to voltage supply source -1 in a knownmanner for providing the flow of an electron current between theseelements. In a similar manner, an electron beam 42 is emitted intoelectron bombardment chamber 22 by another anode-cathode arrangementpositioned across bombardment chamber 22.

Mass spectrometer also includes a vacuum pump 44 for maintaining arelatively high vacuum in evacuatable chamber 14. The ions generatedupon ionization of the two gas samples in electron bombardment chambers20, 22 are respectively accelerated by repeller electrodes 24, 26, andare emitted through aperture 16 to form a single beam of ions containingions from both samples. This beam of ions is then focused by a pair ofbeam centering electrodes 48, 50 and a pair of ground electrodes 52, 54,so that the beam passes through a ground slit 56 and is projected tocollector assembly 13.

The collector assembly 13 includes an outlet aperture 58 and a collectorelectrode 60, which are respectively connected to voltage supply sourceS-1 and a detector D1 of known design. Each of the electrodes 48, 50,52, 54, as well as evacuatable chamber 14, is electrically connected tovoltage supply source S-] in a known manner.

Thus, upon introduction of electron beams 32, 42, into electronbombardment chambers 20, 22, the two gas samples present in bombardmentchambers 20, 22 are ionized and accelerated by the arcuate repellerelectrodes 24, 26 thereby propelling the ions through the funnel-shapedaperture 16 in ionization chamber 12. It has been found that byseparately controlling the voltage signal applied to the chamber walls23, 25, optimum performance of each bombardment chamber 20, 22 may beobtained even though there is a slight variation in the geometricaldimensions of the bombardment chamber 20, 22. The ions from the gassamples are accelerated and focused into a single beam containing ionsgenerated from both samples. Accordingly, an increase in the partialpressure applied to the gas sample in electron bombardment chamber 20has substantially no effect on the number of ions generated by the gassample in electron bombardment chamber 22, and similarly, an increase inthe partial pressure applied to the gas sample in bombardment chamber 22has substantially no effect on the number of ions generated by the gassample in chamber 20. As is apparent, the energy level of electron beam32 may be set equal to the energy level of the electron beam 42, orthese energy levels may be set at different values, depending on thenature of the spectrometric analysis to be conducted.

Although the invention has been shown in connection with a preferredembodiment, it will be readily apparent to those skilled in the art thatvarious changes in form and arrangement of parts may be made to suitrequirements without departing from the spirit and scope of theinvention.

Having now described my invention, I claim:

1. An ion source for a mass spectrometer comprising:

a. an evacuable ionization chamber;

b. inlet means for introducing a plurality of vaporized samples intoseparate regions of said chamber;

c. common aperture means defining at least one opening in communicationwith said ionization chamber through which ions formed in each of saidregions exit to form an ion beam;

= d. partition means within said chamber for restricting the movement ofthe vaporized samples between said regions;

e. means for developing ions of the samples in their respective regionsof said chamber;

f. electrode means for accelerating the ions through said commonaperture means thereby producing an ion beam containing ions from eachof the samples; and,

g. said partition means extending to a position adjacent said commonaperture means to define flow paths whereby ions from each of saidregions may exit said ionization chamber through said opening withoutpassing through any other regions.

2. The apparatus of claim 1 wherein said common aperture means comprisesa single centrally located opening communicating with said ionizationchamber, and said partition means divides said ionization chamber intosubstantially symmetrical regions of substantially equal size.

3. The apparatus of claim 1 wherein said opening has edges shaped tofacilitate the flow of ions from said ionization chamber and theformation of a single ion beam.

4. The apparatus of claim 1 wherein the portion of said partition meanswhich extends in the region of said opening is shaped to facilitate theflow of ions from said ionization chamber and the formation of a singleion beam.

5. The apparatus of claim 4 wherein said portion comprises edges taperedtoward the region of said opening to provide said portion with asubstantially pointed configuration.

6. The apparatus of claim 1 wherein:

said partition means divides said chamber into first and second electronbombardment chambers; and

said inlet means comprises first and second inlet passage means forrespectively introducing first and second vaporized samples into saidfirst and second electron bombardment chambers.

7. The apparatus of claim 6 wherein said partition means extendsadjacent said opening in a plane which is substantially perpendicular tothe plane of said openmg.

8. The apparatus of claim 7 wherein the portion of said partition meanswhich extends in the region of said opening, and the edges of saidopening are shaped to facilitate the flow of ions from said ionizationchamber and the formation of a single ion beam.

9. The apparatus of claim 1 wherein said aperture means comprises an ionexit slit, the edges of which are tapered to facilitate the flow of ionsfrom said ionization chamber and the formation of a single ion beam.

10. The apparatus of claim 1 wherein said electrode means comprises aseparate repeller plate disposed in each of said regions foraccelerating the ions produced in that region into the ion beam.

11. An ion source for separately ionizing a plurality of gas samples,comprising:

a. an ionization chamber having a single aperture through which ions areemitted;

b. inlet means for introducing a plurality of gas samples into separateregions of said chamber;

c. means for developing ions of the samples in their respective regionsof said chamber;

d. partition means within said chamber for restricting the movement ofthe samples between said regions;

e. ion control electrode means in each of said regions for establishingan ion control field for propelling ions through said aperture to form asingle ion beam including ions of each of the samples; and,

f. said partition means extending to a position adjacent said apertureto define flow paths whereby ions from each of said regions may exitsaid ionization chamber through said aperture without passing into anyof the other regions.

12. The apparatus of claim 11 wherein said ion control means in each ofsaid regions comprises a separate ion control electrode positioned ineach of said regions.

13. A method of generating an ion beam containing ions from a pluralityof vaporized samples with an ion source including an ionization chamberpartitioned into separate ionization regions and having a commonaperture means through which ions exit the ionization chamber,comprising the steps of:

introducing a first vaporized sample into a first one of said regions;

introducing a second vaporized sample into a second one of said regions;separately ionizing each of said samples in its respective region byelectron bombardment; and,

accelerating ions produced in each of said regions through said commonaperture means to produce an ion beam containing ions of each of saidsamples.

14. A method of generating an ion beam as defined in claim 13 comprisingthe steps of:

emitting a first electron beam through said first electron bombardmentregion for ionizing the first vaporized sample; and, emitting a secondelectron beam through said second electron bombardment region forionizing the second vaporized sample so that the samples are ionized byseparate electron beams.

1. An ion source for a mass spectrometer comprising: a. an evacuableionization chamber; b. inlet means for introducing a plurality ofvaporized samples into separate regions of said chamber; c. commonaperture means defining at least one opening in communication with saidionization chamber through which ions formed in each of said regionsexit to form an ion beam; d. partition means within said chamber forrestricting the movement of the vaporized samples between said regions;e. means for developing ions of the samples in their respective regionsof said chamber; f. electrode means for accelerating the ions throughsaid common aperture means thereby producing an ion beam containing ionsfrom each of the samples; and, g. said partition means extending to aposition adjacent said common aperture means to define flow pathswhereby ions from each of said regions may exit said ionization chamberthrough said opening without passing through any other regions.
 2. Theapparatus of claim 1 wherein said common aperture means comprises asingle centrally located opening communicating with said ionizationchamber, and said partition means divides said ionization chamber intosubstantially symmetrical regions of substantially equal size.
 3. Theapparatus of claim 1 wherein said opening has edges shaped to facilitatethe flow of ions from said ionization chamber and the formation of asingle ion beam.
 4. The apparatus of claim 1 wherein the portion of saidpartition means which extends in the region of said opening is shaped tofacilitate the flow of ions from said ionization chamber and theformation of a single ion beam.
 5. The apparatus of claim 4 wherein saidportion comprises edges tapered toward the region of said opening toprovide said portion with a substantially pointed configuration.
 6. Theapparatus of claim 1 wherein: said partition means divides said chamberinto first and second electron bombardment chambers; and said inletmeans comprises first and second inlet passage means for respectivelyintroducing first and second vaporized samples into said first andsecond electron bombardment chambers.
 7. The apparatus of claim 6wherein said partition means extends adjacent said opening in a planewhich is substantially perpendicular to the plane of said opening. 8.The apparatus of claim 7 wherein the portion of said partition meanswhicH extends in the region of said opening, and the edges of saidopening are shaped to facilitate the flow of ions from said ionizationchamber and the formation of a single ion beam.
 9. The apparatus ofclaim 1 wherein said aperture means comprises an ion exit slit, theedges of which are tapered to facilitate the flow of ions from saidionization chamber and the formation of a single ion beam.
 10. Theapparatus of claim 1 wherein said electrode means comprises a separaterepeller plate disposed in each of said regions for accelerating theions produced in that region into the ion beam.
 11. An ion source forseparately ionizing a plurality of gas samples, comprising: a. anionization chamber having a single aperture through which ions areemitted; b. inlet means for introducing a plurality of gas samples intoseparate regions of said chamber; c. means for developing ions of thesamples in their respective regions of said chamber; d. partition meanswithin said chamber for restricting the movement of the samples betweensaid regions; e. ion control electrode means in each of said regions forestablishing an ion control field for propelling ions through saidaperture to form a single ion beam including ions of each of thesamples; and, f. said partition means extending to a position adjacentsaid aperture to define flow paths whereby ions from each of saidregions may exit said ionization chamber through said aperture withoutpassing into any of the other regions.
 12. The apparatus of claim 11wherein said ion control means in each of said regions comprises aseparate ion control electrode positioned in each of said regions.
 13. Amethod of generating an ion beam containing ions from a plurality ofvaporized samples with an ion source including an ionization chamberpartitioned into separate ionization regions and having a commonaperture means through which ions exit the ionization chamber,comprising the steps of: introducing a first vaporized sample into afirst one of said regions; introducing a second vaporized sample into asecond one of said regions; separately ionizing each of said samples inits respective region by electron bombardment; and, accelerating ionsproduced in each of said regions through said common aperture means toproduce an ion beam containing ions of each of said samples.
 14. Amethod of generating an ion beam as defined in claim 13 comprising thesteps of: emitting a first electron beam through said first electronbombardment region for ionizing the first vaporized sample; and,emitting a second electron beam through said second electron bombardmentregion for ionizing the second vaporized sample so that the samples areionized by separate electron beams.